<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <script>
        let num1 = prompt('请输入第一个数字: ');
        let num2 = prompt('请输入第二个数字: ');
        let operator = prompt('请输入运算符 (+, -, *, /): ');

        num1 = parseFloat(num1);
        num2 = parseFloat(num2);

        let result;

        switch (operator) {
            case '+':
                result = num1 + num2;
                break;
            case '-':
                result = num1 - num2;
                break;
            case '*':
                result = num1 * num2;
                break;
            case '/':
                result = num1 / num2;
                break;
            default:
                alert('无效的运算符');
        }
        if (result !== undefined) {
            alert('结果: ' + result);
        }
    </script>
</body>
</html>